1. Field of the Invention
The present invention relates to high-density magnetic recording media, and particularly to a flexible magnetic recording medium that is preformatted by magnetic transfer, suitable for high-capacity magnetic disks.
2. Description of the Related Art
With an increase in the quantity of data, there is demand for a magnetic recording medium that is large in memory capacity, low in cost, and capable of high-speed access to a desired block of data. As an example of such a magnetic recording medium, there is known a high-density flexible disk. In realizing the large memory capacity, a so-called tracking servo technique, in which the width of a narrow data track is scanned accurately with a magnetic head to generate signals at a high signal-to-noise ratio (S/N ratio), plays an important role. In the tracking servo technique, a tracking servo signal, an address data signal, a reproduction clock signal, etc., are xe2x80x9cpreformattedxe2x80x9d, that is, recorded in advance, on a disk at predetermined intervals along one rotation thereof.
The magnetic head is accurately positioned over a desired data track by reading out the above-described preformatted signals and then correcting its position. Existing pre-formats are recorded on disks one sheet at a time, one track at a time, with a dedicated servo recorder.
However, the dedicated servo recorder is expensive. In addition, pre-formatting is time-consuming and therefore occupies a large part of the manufacturing cost. For the purpose of reducing the cost, methods have also been proposed, in which pre-formatting is performed no tone track at a time, but by magnetic transfer.
As disclosed in Japanese Unexamined Patent Publication No. 63(1988)-183623 and U.S. Pat. No. 6,347,016, for example, a microscopic xe2x80x9cland/groovexe2x80x9d pattern corresponding to data signals is formed in the surface of a substrate. The surface of a master carrier, equipped with a ferromagnetic thin film formed on at least the lands of the land/groove pattern, is brought into contact with the surface of a magnetic recording sheet or a disk which has a ferromagnetic thin film or ferromagnetic powder coated layer. In this state, by applying an AC bias magnetic field or a DC magnetic field and exciting the ferromagnetic material of the land portions, a magnetization pattern corresponding to the land/groove pattern is magnetically transferred to the magnetic recording medium.
In the above-described method, the lands of a land/groove pattern formed in the master carrier are brought into intimate contact with a magnetic recording medium to be preformatted, and at the same time, the ferromagnetic material constituting the lands is excited. In this way, a predetermined format is formed in the magnetic recording medium. Because magnetic recording can be performed statically without changing the relative position between the master carrier and the magnetic recording medium, accurate pre-formatting can be performed and the time required for pre-formatting is extremely short.
As described above, the magnetic transfer is advantageous in that it can perform pre-formatting accurately and in a short time. However, if magnetic transfer is performed repeatedly on a magnetic recording medium, the master carrier surface will be flawed by an abrasive contained in the magnetic recording medium. As a result, the quality of recorded signals will be degraded and it will become difficult to perform recording on a plurality of magnetic recording disks or a long tape length. Since the abrasive in the magnetic recording medium is indispensable to maintain the high electromagnetic transfer characteristic and durability of the magnetic recording medium, the above-described problem cannot be overcome by simply reducing the quantity of the abrasive.
In addition, if magnetic transfer is performed repeatedly on magnetic recording mediums, there is another problem that the master carrier surface will be gradually corroded by vinyl chloride, etc. contained in the magnetic recording medium and therefore the quality of signals recorded will be degraded.
To enhance the quality of transfer in the above-described magnetic transfer, it is necessary to make the gap between the master carrier and the magnetic recording medium uniform. However, as it is difficult to keep the gap uniform over the entire surface, the master carrier and the slave medium are usually brought into intimate contact with each other. Even in this case, it is extremely important to keep the intimate contact uniform over the entire surface. If there is an imperfect contact portion, magnetic transfer will not be performed on that portion. If magnetic transfer is not performed, then signal dropouts will occur in the magnetic data transferred to the magnetic recording medium and therefore signal quantity will be degraded. In the case where the signals recorded are servo signals, the tracking function is not sufficiently obtained. As a result, there is a problem that reliability will be reduced.
The contact between the magnetic recording medium and the master carrier can be enhanced by pressing the entire back surface of the master carrier with uniform pressure by elastic means (see Japanese Unexamined Patent Publication No. 7(1995)-78337)
The master carrier is usually generated by a lithographic method, a stamper method, etc. Since the master carrier generated by these methods has a warp of about a few 10 micrometers to a few 100 micrometers, it is difficult to apply uniform pressure to the entire surface. Therefore, it is contemplated that it is difficult to apply uniform pressure to the entire surface by simply removing a warp in the master carrier.
In addition, if a magnetic disk is rotated at high speeds, and a magnetic head is repeatedly positioned over the required data track on the magnetic disk over a predetermined time (e.g., 200 to 300 hours in a high-temperature environment), then there are cases where flaws will occur in the disk surface, data cannot be recorded or reproduced, and errors will occur. One of the causes of flaws in the magnetic disk surface lies in a reduction in the performance of a lubricant for the magnetic disk due to volatilization. That is, a lubricant is indispensable for magnetic disks, because it has a great influence on the durability and flaw-resisting property of the magnetic disks.
However, when tracking servo signals, an address data signal, a reproduction clock signal, etc., are prerecorded on a magnetic disk by a master carrier (magnetic transfer), a lubricant for the magnetic disk is accumulated on the master carrier and makes it difficult to magnetically transfer the signals to the magnetic disk.
That is, while a lubricant is required to maintain the durability and flaw-resisting property of the magnetic disk, the lubricant is obstructive when predetermined signals are prerecorded on a great number of magnetic disks by a master carrier.
The present invention has been made in view of the above-described circumstances.
Accordingly, a first object of the present invention is to provide a flexible magnetic recording medium that is capable of increasing the number of magnetic transfer cycles, by preventing flaws from occurring in the surface of a master carrier while maintaining the high electromagnetic transfer characteristics and durability of the magnetic recording medium.
A second object of the invention is to provide a flexible magnetic recording medium that is capable of increasing the number of magnetic transfer cycles, by preventing the surface of a master carrier from being corroded.
A third object of the invention is to provide a flexible magnetic recording medium which is capable of reducing signal dropouts during magnetic transfer and enhancing signal quality, by making the intimate contact between the recording medium and a master carrier sufficient.
A fourth object of the invention is to provide a flexible magnetic recording medium and a fabrication method thereof which are capable of assuring the long-term stability of the quality of recorded signals, by preventing a lubricant for the recording medium from being transferred to a master carrier where predetermined signals are prerecorded by magnetic transfer, while maintaining the durability and flaw-resisting property of the magnetic recording medium.
To achieve the aforementioned objects and in accordance with the present invention, there is provided a first flexible magnetic recording medium to which data is transferred by being brought into intimate contact with a master carrier which has a land/groove pattern corresponding to the data and also has a surface whose Moh""s hardness is 6 to 10. The magnetic recording medium comprises a substrate, anon-magnetic layer, and a magnetic layer. The non-magnetic layer and the magnetic layer are coated on the substrate in the recited order. The magnetic layer contains an abrasive comprising diamond particles whose average particle size is 0.03 to 0.5 xcexcm. The diamond particle content of the abrasive is in a range of 0.1 to 5 wt % of ferromagnetic powder contained in the magnetic layer.
In the first flexible magnetic recording medium of the present invention, the average particle size of the diamond particles is in a range of 0.03 to 0.5 xcexcm and preferably in a range of 0.05 to 0.3 xcexcm. The diamond particle content is in a range of 0.1 to 5 wt % of the ferromagnetic powder and preferably in a range of 0.3 to 3 wt %.
Further in accordance with the present invention, there is provided a second flexible magnetic recording medium to which data is transferred by being brought into intimate contact with a master carrier which has a magnetic pattern corresponding to the data. The second magnetic recording medium comprises a non-magnetic substrate, a non-magnetic layer, and a magnetic layer. The non-magnetic layer and the magnetic layer are formed on the substrate in the recited order. The magnetic layer includes polyurethane resin which contains in a range of 0.05 to 0.7 meq/g at least one kind of polar group selected from the group consisting of xe2x80x94SO3M, xe2x80x94OSO3M, xe2x80x94Pxe2x95x90O(OM)2, xe2x80x94Oxe2x80x94Pxe2x95x90O(OM)2, and xe2x80x94COOH (where M represents a hydrogen atom, alkali metals, or an ammonium salt). The polyurethane resin content is 60 wt % or greater of the quantity of all resins in the magnetic layer.
In the second flexible magnetic recording medium of the present invention, the aforementioned one kind of polar group is in a range of 0.01 to 0.7 meq/g, preferably in a range of 0.1 to 0.5 meq/g, and further preferably in a range of 0.2 to 0.4 meq/g.
The aforementioned polyurethane resin content is 60 wt % or greater of the quantity of all resins in the magnetic layer and preferably 70 wt % or greater. It may be 100 wt %. That is, all resins in the magnetic layer may be polyurethane resin.
Further in accordance with the present invention, there is provided a third flexible magnetic recording medium to which data is transferred by being brought into intimate contact with a master carrier which has a land/groove pattern corresponding to the data. The third magnetic recording medium comprises a non-magnetic substrate, and a non-magnetic layer and a magnetic layer coated on the substrate in the recited order. The relationship between the Moh""s hardness (X) of the surface of the master carrier and the Knoop hardness (Y kg/mm2) of the surface of the magnetic recording medium is represented as 1xe2x89xa6Y/Xxe2x89xa67.
The Knoop hardness of the surface of the magnetic recording medium is measured by a Knoop hardness test. When the length of the longer diagonal of a rhombic indentation produced with a load of P kg by a diamond indentator is designated as l, the Knoop hardness is expressed as 14.22 P/l2 (kg/mm2).
Further in accordance with the present invention, there is provided a fourth flexible magnetic recording medium to which data is magnetically transferred by being brought into intimate contact with a master carrier which has a land/groove pattern corresponding to the data. The fourth magnetic recording medium comprises a substrate, and a non-magnetic layer and a magnetic layer coated on the substrate in the recited order. In the fourth magnetic recording medium, a first coating solution for forming the non-magnetic layer contains a first lubricant in a range of 1 to 20 wt % of non-magnetic powder contained in the non-magnetic layer. A second coating solution for forming the magnetic layer contains a second lubricant which is xc2xc or less of the first lubricant in quantity. The first and second lubricants are liquids at a temperature at which the magnetic transfer is performed.
The first lubricant and the second lubricant may be the same or different in kind, if they are liquids at a temperature at which the magnetic transfer is performed.
The first lubricant is in a range of 1 to 20 wt % of the non-magnetic powder, preferably in a range of 2 to 15 wt %, and further preferably in a range of 4 to 10 wt %. The second lubricant is xc2xc or less of the first lubricant in quantity and preferably {fraction (1/10)} or less in quantity.
Further in accordance with the present invention, there is provided a method of fabricating a flexible magnetic recording medium, which comprises (1) a step of stacking a non-magnetic layer which contains in a range of 1 to 20 wt % of non-magnetic powder a first coating solution being a liquid at a temperature at which magnetic transfer is performed, and a magnetic layer which contains a second coating solution being xc2xc or less of the first lubricant in quantity and also being a liquid at the temperature, on a substrate in the recited order; (2) a step of bringing a master carrier, which has a land/groove pattern corresponding to data to be transferred, into intimate contact with the stacked body to transfer the data to the stacked body; and (3) a step of treating the stacked body with heat.
In the above-described first flexible magnetic recording medium, the magnetic layer contains an abrasive comprising diamond particles whose average particle size is 0.03 to 0.5 xcexcm. The diamond particle content of the abrasive is in a range of 0.1 to 5 wt % of ferromagnetic powder contained in the magnetic layer. The first flexible magnetic recording medium has the following advantages: the surface of the master carrier is prevented from being flawed by the magnetic recording medium during magnetic transfer; the long-term stability of the quality of signals recorded on the magnetic recording medium can be achieved; and the running durability of the magnetic recording medium can be maintained.
In the above-described second flexible magnetic recording medium, the magnetic layer includes polyurethane resin which contains in a range of 0.05 to 0.7 meq/g at least one kind of polar group selected from the group consisting of xe2x80x94SO3M, xe2x80x94OSO3M, xe2x80x94Pxe2x95x90O(OM)2, xe2x80x94Oxe2x80x94Pxe2x95x90O(OM)2, and xe2x80x94COOH (where M represents a hydrogen atom, alkalimetals, or an ammonium salt). The polyurethane resin content is 60 wt % or greater of the quantity of all resins in the magnetic layer. Therefore, the master carrier surface can be prevented from being corroded during magnetic transfer by a chemical substance, which can be the cause of corrosion, such as vinyl chloride contained in the magnetic recording medium. As a result, the long-term stability of the quality of signals recorded on the magnetic recording medium can be achieved.
In the above-described second flexible magnetic recording medium, polyurethane resin with a high polar group content is employed a predetermined quantity or greater. Therefore, the dispersion of magnetic powder in the magnetic layer can be enhanced, and uniform dispersion can be achieved. As a result, it becomes possible to obtain a sufficient S/N ratio.
In the above-described third flexible magnetic recording medium, the relationship between the Moh""s hardness (X) of the surface of the master carrier and the Knoop hardness (Y kg/mm2) of the surface of the magnetic recording medium is represented as 1xe2x89xa6Y/Xxe2x89xa67. Therefore, magnetic transfer can be performed while holding a sufficient intimate contact between the master carrier and the magnetic recording medium. As a result, signal dropouts can be prevented from occurring in magnetic data transferred to the magnetic recording medium, and signal quantity can be enhanced.
In the above-described fourth flexible magnetic recording medium, the first coating solution for forming the non-magnetic layer contains a first lubricant in a range of 1 to 20 wt % of non-magnetic powder contained in the non-magnetic layer. The second coating solution for forming the magnetic layer contains a second lubricant which is xc2xc or less of the first lubricant in quantity. Therefore, the second lubricant can be prevented from being transferred to the master carrier, and the long-term stability of the quality of signals recorded on the magnetic recording medium can be achieved. In addition, the first and second lubricants are liquids at a temperature at which the magnetic transfer is performed. Therefore, the lubricant moves gradually from the non-magnetic layer to the magnetic layer after magnetic transfer and during rotation of the magnetic recording medium. As a result, it becomes possible to maintain the durability and flaw-resisting property of the magnetic recording medium.
In the above-described fabrication method, the non-magnetic layer and the magnetic layer are stacked on a substrate in the recited order. Then, a master carrier, which has a land/groove pattern corresponding to data to be transferred, is brought into intimate contact with the stacked body to transfer the data to the stacked body. Next, the stacked body is treated with heat. Therefore, since the lubricant in the non-magnetic layer can be efficiently moved to the magnetic layer (overlying layer), the durability and flaw-resisting property of the magnetic recording medium can be further enhanced.